1. Field of the Invention
This invention relates to a linear motion rolling guide unit applied to a machine tool, an industrial robot, a precision machining apparatus and a semiconductor manufacturing apparatus, wherein rolling elements rolling between raceway grooves formed in a track rail and a casing which are adapted to be moved slidingly with respect to each other are retained by retainer bands.
2. Description of the Prior Art
There is a known linear motion rolling guide unit shown in FIGS. 8 and 9. This linear motion rolling guide unit is formed by a track rail 2 provided with raceway grooves 4 in both of longitudinal side surfaces 3 thereof, and a slider 1 saddled slidably on the track rail 2. The slider 1 is slidable relatively to the track rail 2 and has a casing 5 provided in the portions thereof which are opposed to the raceway grooves 4 with raceway grooves 9, balls 7 constituting a plurality of rolling elements fitted relatively movably between the opposed raceway grooves 4, 9, and end caps 6 fixed to both ends with respect to the sliding direction, i.e. longitudinal direction of the casing 5. Side seals 17, which attain the sealing of narrow clearances between the track rail 2 and slider 1, are attached to the end caps 6, and grease nipples 23 for supplying a lubricant to the slide surfaces between the track rail 2 and slider 1 are also fixed to the same.
In order to prevent the balls 7 from falling from the casing 5, retainer bands 15 are fixed to the slider 1 so as to surround the balls 7. The track rail 2 is provided with retainer band grooves 16 extending along the raceway grooves 4 in the side surfaces 3. As shown in FIG. 10, the conventional retainer band 15 is provided in the casing 5 so that the retainer band 15 extends along the relative raceway groove 9 in the casing 5 and is loosely fitted in the relative retainer band groove 16 in the track rail 2. The retainer band 15 is formed to a rectangular cross sectional shape, or formed by using a rod material to a circular or semicircular cross-sectional shape (refer to, for example, Japanese Utility Model Publication No. 26577/1988).
Lower seals 8 are provided on the casing 5 so as to reliably prevent the balls 7 from falling from the casing 5 and seal both of the longitudinal side surfaces 3 of the casing 5 and track rail 2 and a lower surface of the casing 5. The slider 1 is provided in a saddled state on the track rail 2, and adapted to be slid freely via the balls 7 circulating along the raceway grooves 4 in the track rail 2. The balls 7 in load regions which roll in the raceway grooves 4 in the track rail 2 are introduced into direction changing passages 11 formed in the end caps 6, and they are then moved into return passages 12 formed above and in parallel with the raceway grooves 9 in the casing 5, whereby a plurality of balls 7 are circulated endlessly in the endless circulating passages. Owing to such rolling movements of the loaded balls 7 positioned between the raceway grooves 9 formed in the casing 5 and those 4 formed in the track rail 2, the slider 1 can be slid relatively to the track rail 2.
Japanese Utility Model Publication No. 26577/1988 also discloses ball retainers for linear motion ball bearings. These ball retainers comprise thin metal rod materials the height of a cross section of which is larger than the width of the rod materials, and are positioned close to the outer sides of the balls on the raceway surfaces of a slide unit. Each ball retainer is formed to a lip-carrying C-shaped structure comprising a straight rod type main portion fixed in parallel with the balls, bent portions connected to both ends of the main portion at right angles thereto, and short hook portions bent in the shape of lips in the inward direction from and joined to free ends of the bent portions. The ball retainer is held in a hooked state on the slide unit owing to the elastic force of the thin rod type main portion and bent portions. The ball retainer has a cross-sectionally rectangular shape shown in FIG. 10.
Japanese Utility Model Laid-Open No. 171722/1988 discloses a linear guide apparatus. A wire retainer in this linear guide apparatus is provided with an axially extending wire retaining bore in a base portion of a ball scooping projection of an end cap. It is further provided with a ball guide portion comprising a linear part, and arcuate parts at both ends of the linear part, and fixing portions parallel-extending axially from the ends of the arcuate parts and inserted through the wire retaining bore. This publication discloses a circular or plate type wire retainer.
Japanese Patent Laid-Open No. 370414/1992 discloses a linear motion rolling guide unit having a high sealability. In this linear motion rolling guide unit, it is necessary that the sealing performance thereof be improved. In order to meet this requirement, retainer band fitting grooves in a track rail are grind-finished by a grindstone. In order to carry out such a machining process easily, the retainer band fitting grooves are formed to a trapezoidal cross-sectional shape.
Japanese Utility Model Laid-Open No. 92522/1989 discloses a cross roller type linear motion rolling guide unit in which the rotational axes of adjacent rollers constituting rolling elements cross each other at 90.degree. alternately. In this linear motion rolling guide unit, the inner surfaces of retainers are formed as right-angled V-shaped groove surfaces so as to support the angled portions of the crossed rollers.
In recent years, a compact linear motion rolling guide unit of smaller dimensions having a large load capacity has been demanded. To meet this demand, the length of a casing of a slider is increased to obtain a large load capacity but the length of ball retaining bands increases accordingly and necessarily. When the retainer bands become longer, they become liable to be bent, so that the balls fall from the raceway grooves in the casing.
The conventional retainer bands are formed to a rectangular cross-sectional shape as shown in FIG. 10, or formed by using a rod material to a circular or semicircular cross-section 1 shape. The retainer bands 15 are usually tensed so as to hold a plurality of balls 7 and prevent them from falling from the raceway grooves in the casing 5. However, when the retainer bands 15 are deformed during an operation for setting the slider 1 on the track rail 2 or removing the former from the latter, so that distances between the terminal corner portions of a raceway groove 9 in the casing 5 and the corner portions of a side surface of the relative retainer band 15, i.e. the distances C, D become larger than the diameter of each ball 7, the balls 7 necessarily fall from the raceway groove 9 in the casing 5.
In recent years, the reduction of the cost of manufacturing a linear motion rolling guide unit has progressed, and the retainer band fitting grooves formed in a track rail tend to be formed shallowly. Moreover, the lengths of a casing and retainer bands have increased because of the necessity of increasing the load capacity as mentioned above. This causes a decrease in the rigidity of the retainer bands, and the retainer bands to be deformed. Consequently, the balls fall from the raceway grooves.